Field of the Invention:
The invention relates to electronic devices, and particularly to electronic switching devices.
Semiconductor components are used in addition to mechanical switchgear for switching electric currents. Semiconductor components can be divided into current-controlled semiconductor components, including bipolar transistors and thyristors, on the one hand, and voltage-controlled semiconductor components such as, for example, the unipolar MOS (Metal Oxide Semiconductor) field-effect transistors (MOSFET), or the bipolar MOS-controlled thyristors (MCT), or the MOS-controlled bipolar transistors (IGBT), on the other hand. All of these semiconductor components can only switch currents in one current direction, that is to say only for a specific polarity of the operating voltage (switchable state). In the switchable state, by alteration of the control voltage or of the control current, the semiconductor component can be switched from an off state, in which virtually no current flows through the semiconductor component, into an on state, in which a current flows through the semiconductor component, or vice versa. In the on state, the current flowing through the semiconductor component is dependent on the magnitude of the operating voltage and the driving control voltage or the driving control current. In its off state, each semiconductor component can be reverse-biased only up to a maximum reverse voltage (breakdown voltage). A charge carrier breakdown occurs at higher reverse voltages and may rapidly lead to the destruction of the component. For alternating currents, two semiconductor components are, as a rule, reverse-connected in parallel (bidirectional connection).
Silicon (Si) is used, in practice, as the semiconductor material for semiconductor components, in particular for power electronics. One of the reasons is that silicon process technology is highly developed. Also, voltage-controlled MOS semiconductor components using silicon have high switching speeds owing to the high charge carrier mobility of silicon in the channel region of the MOS structure. One problem of MOSFETs is that the steady-state losses in the on state become higher, the higher the reverse voltages to be managed by the MOSFET in the off state are. In silicon, the steady-state power loss of a power MOSFET which is designed for high reverse voltages starting from about 600 V becomes so high at forward currents starting typically from about 5 A that bipolar IGBTs in silicon are preferred to the silicon MOSFETs for these and higher switching currents and reverse voltages.
The international publication WO 95/24055 discloses a MOSFET which is formed in the semiconductor material of silicon carbide (SiC). Given the same blocking capability of more than 600 V, such a silicon carbide MOSFET can be designed with lower on-state losses than a silicon MOSFET. However, the process technology in silicon carbide, in particular for the MOS structure, is not yet as advanced as in silicon. The result is that silicon carbide MOSFETs are not yet mass produced.